The use of thymidine-2-C14 in the study of human gingiva in vitro.

Human gingival explants were cultured for 1 or 2 days in a natural medium without serum. After 1 day in vitro the explants were partly encircled by epithelium which had proliferated from the cut edges of the explant and from rete ridges near the cut edge (epiboly). There was also some cell division in the cells of the spinous layer, and a thick parakeratotic layer had developed. These areas of proliferation were disclosed by the uptake of thymidine-2-C14 by the epithelial cells. Degenerative changes were also evident after 1 day in vitro. This began as hydropic degeneration in the spinous layer of the epithelium and resulted in almost total acantholysis and desquamation of the spinous layer after 2 days in vitro. The addition of serum to the medium might have promoted more epithelial proliferation and delayed the degeneration. The use of thymidine-2-C14 in the medium was an effective method of labeling the active epithelial cells.